Non-photosensitive polyimide materials have been widely used in passivation layer formation processes for semiconductor devices manufacturing due to their good high-temperature resistance, excellent mechanical and electrical properties and high chemical stability. The use of non-photosensitive polyimide materials can reduce the damages to semiconductor devices generated from various natural environments and operating environments and thus improve the reliability and stability of the resultant semiconductor devices.
FIG. 1 is a flow chart illustrating a conventional method of manufacturing a non-photosensitive polyimide passivation layer. The method includes: spin-coating a non-photosensitive polyimide layer over a wafer on which a non-photosensitive polyimide passivation layer is to be formed and then baking it; spin-coating a photoresist layer over the non-photosensitive polyimide layer and baking it; removing exposed portions of the photoresist layer as well as corresponding portions of the non-photosensitive polyimide layer thereunder in a development step by an exposure-and-development process to form a desired pattern both in the photoresist layer and the non-photosensitive polyimide layer; removing the unexposed portion of the photoresist layer by using a photoresist stripper; and forming an imidized polyimide passivation layer by curing the patterned non-photosensitive polyimide layer. However, in research and practical use, this method has been found to have some drawbacks as shown in FIGS. 2 to 4.
Firstly, in the development step, in order to ensure a sufficient development for a non-photosensitive polyimide layer, the non-photosensitive polyimide layer is generally developed for a relatively long time. Such over-development may lead to the corrosion (as shown in FIG. 2) of aluminum PAD situated under some portions of the non-photosensitive polyimide layer having a smaller thickness than other portions by the developer, thus affecting the performance of the semiconductor device.
Secondly, in the development step, due to the isotropic development behavior of the developer, simultaneous with the development of the non-photosensitive polyimide layer by the developer in an intended direction, namely, the direction of the thickness of the layer (i.e., the vertical direction), the same extent development will also proceed from each lateral side of the non-photosensitive polyimide layer (i.e., the developer develops the non-photosensitive polyimide layer both in the vertical and lateral directions with same development rate). This effect will lead to a tapered and uncontrollable profile of the resultant non-photosensitive polyimide pattern (as shown in FIG. 3), which not only affects the performance of the device, but is also adverse to the miniaturization of the device as it requires comparatively big intervals between the openings (for forming pads therein) formed in the passivation layer.
Thirdly, commonly used solvents (for example, N-methylpyrrolidone (NMP)) for non-photosensitive polyimide also have a high dissolving capacity for the photoresist, thus after spin-coating the photoresist layer on the non-photosensitive polyimide layer, a portion of the photoresist will be dissolved in the non-photosensitive polyimide layer which is difficult to be removed by a photoresist stripper in a subsequent process. Therefore, photoresist residues (shown in FIG. 4) will remain in the patterned non-photosensitive polyimide layer.